When Marcus becomes anxious, he eats a tremendous amount of food over an extended period of time. Afterward, Marcus feel guilty about his binge eating but does not purge or exercise excessively. What is Marcus demonstrating?
Binge eating syndrome
I would diagnose binge-eating syndrome.
At first glance, this may sound like bulimia nervosa, but remember, the characteristic of bulimia is purging (vomiting, et cetera). Since he does not purge, BED is my diagnosis.